1. Field of the Invention
The present invention relates generally to the use of exfoliated clay nanoplatelets, and more particularly to a method for making an electrolyte composition of a dye-sensitized solar cell utilizing exfoliated clay nanoplatelets, and a method for instantly encapsulating cations.
2. Description of Related Art
Clay is a natural material with a layered structure, which is mainly composed of layered silicate and has excellent heat resistance, chemical corrosion resistance and low expansion coefficient. Cations entrapped between clay layers are such as Li+, Na+, K+, Ca2+, Mg2+, Ba2+, La3+, Ce2+. In the prior art, a cationic surfactant is usually used as an intercalation agent, which is mixed with a monomer and inserted between the clay layers for polymerization so as to disperse the clay layers, which, however, only increases the distance between the clay layers without achieving complete exfoliation of the clay layers.
Taiwan Patent No. I284654 discloses a fabrication method of clay nanoplatelets, wherein a water-soluble initial agent, a polar monomer and a layered clay material are used for emulsifier-free emulsion polymerization, and then a solvent is used to remove the polymer matrix so as to form clay nanoplatelets. However, the patent does not disclose the application of the clay nanoplatelets.
Taiwan Patent No. 200844148 discloses preparation of exfoliated clay/polymer nanocomposite latex for use in waterproof gas-barrier materials or gas-barrier coatings or electronic materials. U.S. Pat. No. 5,998,528 discloses a carrier composition comprising a layered material (phyllosilicate), a polymer intercalated between layers of the layered material, an organic liquid and cations. The carrier composition can be used as a carrier material or used for delivery of an active compound such as a drug or cosmetic, wherein the intercalated complex can be exfoliated prior to combination with the organic liquid. Taiwan Patent No. I288648 discloses an inhibitor for harmful micro-organisms, wherein the inhibitor comprises completely exfoliated silicon nanoplatelets and a medium or carrier. The inhibitor is used for encapsulating bacteria so as to suppress the activity of the bacteria.
Currently, the third generation of organic solar cells, e.g. dye-sensitized solar cells (DSSCs) have been developed. Such a dye-sensitized solar cell has a photoelectric conversion efficiency close to that of a crystalline silicon solar cell, but has a relatively simple fabrication process and low fabrication cost. Meanwhile, the dye-sensitized solar cell can be made semi-transparent and accordingly is suitable to be applied to buildings or other goods. Therefore, the research and development of the dye-sensitized solar cells have received considerable attention. To fabricate a dye-sensitized solar cell, TiO2 nanoparticles are porously coated on a transparent conductive substrate such as a conductive glass to function as an anode, and platinum is sputtered on another transparent conductive substrate such as a conductive glass to function as a cathode, a dye sensitizer is chemically adsorbed onto the TiO2 nanoporous structure and finally an electrolyte is added between the anode and cathode.
The electrolyte can be such as a liquid electrolyte, which has a high ion conductivity and provides the dye-sensitized solar cell with a high efficiency. However, the liquid electrolyte easily volatilizes, leaks or dries under scorching of sunlight in long term use of solar cells. A solid electrolyte such as a P-type semiconductor (CuSCN, CuI) or hole transmission material (OMeTDA) overcomes the drawbacks of the liquid electrolyte, but has a high fabrication cost and low photoelectric conversion efficiency. A gel polymer electrolyte is formed by adding a polymer into a liquid electrolyte and the remaining solvent is also easy to volatilize. An ionic liquid electrolyte is non-toxic, has low volatility, excellent thermal stability and high dielectric constant and accordingly has become a development trend of the dye-sensitized solar cells. However, the ion liquid electrolyte is also easy to leak. Therefore, there is still a need to develop an electrolyte composition for dye-sensitized solar cells to overcome the conventional drawbacks of volatility and leakage of electrolyte.
Taiwan Patent No. I284654, No. 200844148, No. I288648 and U.S. Pat. No. 5,998,528 do not suggest or teach the use of exfoliated clay in an electrolyte for solar cells.
Taiwan Patent No. 586248 discloses a gel electrolyte for a lithium secondary battery, which comprises a clay and a gel polymer, wherein the clay is lipophilically modified by a surfactant, the gel polymer is intercalated with the clay in the presence of a plasticizer, and a lithium salt is added thereto so as to form a gel electrolyte. The patent uses the gel polymer to achieve a gel effect, but the patent only increases the distance between the clay layers without achieving complete exfoliation of the clay layers. Therefore, the clay of the patent is not an exfoliated clay.
Therefore, the industry is still not familiar with the encapsulation property of the exfoliated clay and the application of the exfoliated clay in solar cells. On the other hand, there is an urgent need to develop a technology for rapidly encapsulating cations and overcoming the conventional drawbacks of volatility and leakage of electrolyte.